Many imageable materials and imaging technologies are commercially available today. The most useful of these technologies tend to have photosensitive capabilities which enable convenient reproduction of images. This is particularly true in the micrographics and graphic arts field.
The most commonly used imaging systems are based on silver halide emulsion technology, diazonium salt technology, or photopolymerizable composition technology. Each of these different systems has its own advantages and problems.
Silver halide films are the most widely used graphic arts material. These films show high resolution, high imaging speeds, and consistency in their performance. However, because of the rising cost of silver, systems using silver halide emulsions are becoming economically disadvantageous. Silver halide films also have other disadvantages including the requirement for multiple steps in processing, unstable processing solutions, and lack of dimensional stability.
Imaging systems using diazonium salt compositions provide high resolution and are considerably less expensive than silver to produce. The visible image produced by most diazonium salt systems consists of a dye and tends to have limits on the maximum optical densities or image color obtainable, higher minimum densities than desirable, and often suffers from a low contrast. Although thermally developable diazonium salt systems are available in the marketplace, many diazonium salt image systems still rely upon ammonia development which is undesirable because of the difficulty of working in a closed environment with ammonia. Often the diazo image comprises a dye and is not considered archival in the micrographic context.
Photopolymeric imaging systems are both inexpensive and easy to make. However, these systems usually depend upon the loading of the photopolymeric layer with opacifying material to provide optical density, which tends to reduce the sensitivity of the photosensitive layer.
One type of system which has recently been introduced to the art comprises a substrate having on at least one surface thereof a roughened metallic layer which is overcoated with a metal or metal alloy layer and subsequently coated with a photosensitive resist composition. This type of technology is exemplified by U.S. Pat. No. 4,138,262 wherein a bismuth layer is sputter deposited upon a substrate and a continuous high optical density layer of bismuth or an alloy of bismuth is vacuum deposited on the sputtered metal layer to provide a highly opaque appearance to the surface. This system is developed in two steps by first imagewise exposing the photoresist layer, then dissolving away the photoresist material in an imagewise manner to expose the underlayers of metal. The exposed metal or metal alloy is etched away in a second step. When viewed from the photoresist side, this provides a black metal image on a clear background. When viewed from the opposite side, this provides a shiny metal layer on a clear background. This system requires two separate metal coating steps and requires two developing solutions, one for the photoresist and the other for the metal or metal alloy opaque layer. The system as disclosed is also limited in the metals that can be used. Other systems which utilize photoresist layers over metal or metallized substrates are disclosed in U.K. Pat. No. 1,468,746 wherein substrates of metal are overcoated with photoresist materials. The film is shown to be particularly desirable for microforming images and shown to have outstanding edge acutance and high resolution. The system will only provide images having substantially pure metal features.
U.S. Pat. Nos. 4,008,084 and 4,158,079 show imaging systems using combinations of metals in different layers or different layers of metals and metal oxides under photoresist compositions. The latter patent in particular shows an imaging system comprising a substrate having respectively on at least one surface an aluminum foil layer, an aluminum oxide layer and a photoresist composition. This material suffers from poor bonding of the aluminum oxide layer to the photopolymer layer which causes separation of those layers during development, particularly by aqueous alkaline developers conventionally used with photoresist materials. The juncture between the metal/metal oxide layer has a sharp, discontinuous transition from metal to metal oxide because of the manner in which it is formed.
U.S. Pat. No. 4,158,079 discloses another imageable composite comprising a substrate, an aluminum foil layer, an aluminum oxide layer and a photoresist layer. The aluminum foil layer is adhered to the substrate by an adhesive and the aluminum oxide layer is produced by anodization of the foil. The optical density of the composite is increased by adding coloring material to the aluminum oxide layer prior to applying the photoresist. This composite has the disadvantage of requiring multiple steps in manufacturing of the substrate (both lamination and anodization) and in the fact that addition of a coloring material to the aluminum oxide layer fills the pores of that layer and reduces the ability of the photoresist layer to bond to that surface.